1. Field of the Invention
The present invention relates to the field of fluid heaters, and especially to instantaneous heaters, and more particularly to a thermal and flow regulator for continuous flow liquid heaters.
2. Description of the Prior Art
Constant problems which have been associated with the operation of instantaneous fluid heaters are condensation and sedimentation. Units fired with gas fuel produce water vapor and carbon dioxide. When the flue products contact the heat exchanger, which has a temperature considerably below the dew point, condensation forms along the heat exchanger and moisture drops down on the burners and lining of the fire box, causing serious problems. Sedimentation within the piping is also affected by the liquid temperature, and can be very detrimental.
Liquid entering a heat exchanger has a relatively low inlet temperature. As it flows through the heat exchanger, the temperature of the liquid increases. However, this temperature level is still below the dew point of the flue products, therefore resulting in condensation of moisture on the outside of the exchanger. The temperature rise of the liquid to be heated depends on the flow rate through the heat exchanger tubes. A higher flow rate will result in a lower temperature rise and a lower rate will result in a higher temperature rise. Adjustment of the liquid flow rate can therefore be used to modify the liquid temperature, and consequently the amount of condensation which forms on the exterior of the exchanger.
The deposit of minerals in a liquid is also temperature related, accelerating as the liquid temperature increases. The forming of these mineral deposits will greatly reduce the heat transfer efficiency of the heat exchanger, since the deposits work as an insulator. Furthermore, within a relatively short period of time, the heat exchanger may become quite clogged, causing the entire system to fail.
Common practices to resolve the above-outlined problems are as follows. In one approach, the flow rate is regulated based on the pressure drop across the heat exchanger, using a plunger and spring assembly or constant orifices. In another approach, the flow rate is regulated with a temperature signal, but this has many limitations based on displacement of a sensor, etc.
The present invention reduces condensation and sedimentation substantially. The unique design features lead to the ability to regulate the liquid flow rate based on pressure drop and temperature across the heat exchanger with minimum restrictions.